1. Field of the Invention
The present invention relates to lens barrels and imaging devices, and particularly to a lens barrel including a position detecting mechanism that detects the position of an imaging optical system including a focus lens, a zoom lens, and so on, and an imaging device including this lens barrel.
2. Description of the Related Art
In a video camera device, a movable lens for zooming and a movable lens for focusing are disposed inside a tube in order to achieve a zoom function and an autofocus function, and a drive unit for moving these lenses along the optical axis direction is provided. For accurate control of the driving of the movable lens, the position of the movable lens needs to be accurately detected.
In a related art, the position detection for the movable lens is carried out by a position detecting sensor. As shown in FIG. 15, the position detecting sensor is composed of a position detecting element 6 attached to a tube 4 as a fixed part and a position detection magnet 1 that is so attached to a lens holder 2 for an optical lens 3 as to face the position detecting element 6 and extend along the movement direction of the lens holder 2.
N and S poles of the position detection magnet 1 are so magnetized as to be alternately arranged along the extension direction of the position detection magnet 1 as shown in FIG. 16.
As the position detecting element 6, an MR sensor (magnetoresistive element) is used. The resistance of the magnetoresistive element changes in response to change in a magnetic field. Therefore, upon the movement of the position detection magnet 1 in linkage with the movement of the movable lens, the magnetic field that acts on the position detecting element 6 opposed to the position detection magnet 1 changes and the magnetoresistance value changes.
In linkage with the change in the magnetoresistance value, as shown in FIG. 17, the position detecting element 6 outputs an A-phase detection signal A sin θ that changes in the manner of a sine wave with a predetermined cycle and a B-phase detection signal A cos θ that changes in the manner of a cosine wave that is different in the phase by λ/4 from the A-phase detection signal. The position of the movable lens is detected based on these two detection signals.
The lens holder 2 is so held as to be movable in the tube 4 along the direction of an optical axis L by a guide shaft 5 provided in the tube 4 in parallel to the optical axis L. This lens holder 2 is driven along the direction of the optical axis L by a linear actuator. The linear actuator is composed of a drive coil 7, a drive magnet 8, a grounded yoke 9, and an opposed yoke 10.
Examples of documents relating to the related art include Japanese Patent Laid-open No. 2006-10568 (Patent document 1, hereinafter), Japanese Patent Laid-open No. 2004-221527 (Patent document 2, hereinafter), and Japanese Patent No. 3177931.